Why? Because rarely do they sell the HDTVs which generally have the most highly rated PQ (picture quality).
That said, I prefer Sammy since I have had better post-sales warranty/repair/parts experiences vs Vizio. YMMV. They both mass produce HDTVs, so perhaps it's a matter of which one suits your needs initially (price point to get you in the door). I always feel what happens *after* you buy the HDTV makes the most sense, even if it means spending $500 more. People forget that they keep these devices quite a long time usually, so the extra cost is often moot.
Trying to decide between a vizio or Samsung. 75". sams club will be selling the Samsung UN75JU641DFXZA for $2400 on black Friday. I'm really considering this. Thoughts?